1. Field of the Invention
The invention pertains to the field of variable camshaft timing (VCT) systems. More particularly, the invention pertains to a center mounted spool valve and a lock pin, which is fed directly with supply oil.
2. Description of Related Art
Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more xe2x80x9cvane phasersxe2x80x9d on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor with one or more vanes, mounted to the end of the camshaft, surrounded by a housing with the vane chambers into which the vanes fit. It is possible to have the vanes mounted to the housing, and the chambers in the rotor, as well. The housing""s outer circumference forms the sprocket, pulley or gear accepting drive force through a chain, belt or gears, usually from the crankshaft, or possibly from another camshaft in a multiple-cam engine.
In an effort In traditional systems the locking pin is present in the vane of the phaser. Taking pressure (control pressure) from either the advanced or retard chamber, or a combination of both disengages the locking pin.
A traditional system as shown in prior art FIGS. 1 and 2 comprises an oil pump (10) that provides supply oil to a remotely located spool valve (14) in the engine block (16). The spool valve (14) is controlled by a variable force solenoid (12). Oil lines (18)(20) present in the engine block (16) are supplied with oil from the spool valve (14) and lead into a bearing (22) located on the camshaft (26). The lines (18)(20) continue through the bearing (22) and the camshaft (26) until they terminate in the phaser (24). The two lines are present in the phaser vane, one leading to the retard chamber (17b) and one leading to the advanced chamber (17a), labeled R and A respectively.
In order to prevent motion of the phaser when oil pressure is too low to hold position, a locking pin is often provided. The locking pin (30) of the system can be located in the vane (28) or in the rotor or housing. The locking pin is disengaged from the rotor (not shown) by taking the oil pressure from either the advance or retard chambers or a combination of the two. In an effort to reduce the oscillation of the phaser due to cam torsionals of a remotely mounted spool valve in a traditional system as described below, the spool valve overlap is increased to reduce the flow from the chamber to chamber. In such a system as described, the locking pin (30) only receives partial oil pressure. The partial oil pressure is due to the fact that the oil must travel through the spool valve (14) located in the engine block (16), through lines (18)(20) in both the engine block (16) and the camshaft (26), and through the chambers (17a)(17b) in the phaser (24). As the oil is made to travel further and further, and through more objects, for example through the cam bearings, chambers and the spool valve, the amount of oil lost due to leakage increases and the oil pressure is reduced significantly, so that by the time the oil reaches the locking pin in the above described system, the pressure is only partial.
Also, in an effort to reduce the oscillation of the phaser due to cam torsionals of a remotely mounted spool valve in a traditional system as described, the spool valve overlap is increased to reduce the flow from the chamber to chamber. The reduction of the flow of oil reduces the pressure of the oil that keeps the locking pin disengaged from the rotor. With the reduction of flow, the locking pin can easily engage the rotor, especially if the vane is in the middle of travel.
In most prior art variable cam timing systems, the locking pin is controlled by the oil pressure in the advance or retard chambers, through an oil line from one or both chambers. These chambers pressurize with oil from the output of the spool valve. For example, in U.S. Pat. No. 6,481,402 the camshaft rotor carries a slidable pin that may be locked in a position with respect to the housing that prevents the movement of the rotor relative to the housing. The sliding action of the pin is controlled by the position of the spool valve that is slidable along its axis to selectively control the flow of engine oil into and out of the advance and retard chambers of the housing. Since the spool valve is controlling whether the pin is locked or not, the locking of the pin is not solely a function of engine oil pressure.
A variable camshaft timing phaser having a locking pin directly influenced by engine oil, which is not impacted by any intervening valves. The locking pin is comprised of a tapered pin, which fits into a tapered recess. The locking pin is biased towards engaging by a spring, and is retracted by oil from the engine oil supply. The locking pin remains disengaged from the tapered recess as long as the oil pump is on.